Solvent Effects on the Rates and the Activation Parameters for the Methoxymercuration of p-Substituted Styrenes

Article abstract of DOI:10.1021/jo00198a019

The second-order rate constants and the activation parameters for the methoxymercuration of a series of para-substituted styrenes have been determined in four methanol/p-dioxane mixtures - X_MeOH varied from 1.00 to 0.791.For each styrene log k is a linear function of X_MeOH.The average value of the slopes of the correlation lines is 8.25 +/- 0.32 which suggests the involvement of eight-nine MeOH molecules in the rate-determining transition state.For each solvent identical linear plots of log k vs. ? and ?⁺ are obtained.At 25 deg C, the value of ρ (av -3.26 +/- 0.05) and ρ⁺ (av -2.86 +/- 0.05) are independent of the solvent's composition.For each styrene ΔG^* increases as the methanol concentration decreases; however, δΔG^* is constant.While δΔG^* varies linearly with ? and ?⁺, in no case is δΔH^* linearly related to δΔS^*.In anhydrous methanol this reaction series is isoenthalpic; however, this is not the case for either of the methanol/p-dioxane mixtures.On the basis of the ΔS^* values, the reaction series approaches an isoentropic state as the methanol concentration decreases.